ABSTRACT Colorectal cancer (CRC) is a major cause of morbidity and mortality. It is a heterogeneous disease, with significant epidemiologic and biologic differences depending on the location of the cancer in the colon; specifically, whether the tumors are right-sided or left-sided. Factors that trigger tumorogenesis or contribute to differences in outcomes of this malignancy are poorly understood. Epidemiologic data indicate a higher incidence of right-sided cancers in females, African-Americans, and individuals over 70 years of age, and possibly a higher mortality for right-sided versus left-sided cancers. Differences are attributable to a number of genetic and non-genetic factors, including host genetic interactions, social determinants of health, such as health insurance status and access to screening, diet, and environmental triggers, as well as possible infectious agents. The detection of infectious agents in CRC tissue is increasingly important to establish associations and ultimately discover the pathogenic mechanisms behind this malignancy. Recent reports suggest that viruses, as well as certain bacteria, may be important determinants of CRC. However, the detection and characterization of viruses in CRC tissues has been hampered by the difficulty in culturing or isolating viruses by conventional molecular biology methods. In the proposed prospective pilot study, we seek to conduct comparative metagenomic and metabolomic analyses of healthy (n=50) versus tumorous tissues (n=50) from patients with right-sided versus left-sided CRC. All samples will be collected from patients undergoing curative resection at the Department of Surgery of the University of California, San Diego. We will determine the presence of distinct viral and microbial communities, biofilm layers, and metabolomic profiles in approximately 15 right-sided and 35 left-sided tumors and in the adjacent normal tissue (negative control). Comparative analyses between viral and microbial expression, molecular events and tumor location will be correlated. Metagenomics is a comprehensive technique for surveying microbial species associated with a disease, and combines the power of deep sequencing genomics, bioinformatics, and systems biology. It has been used to describe the microbial content of environmental and clinical samples. Preliminary work by members of our team investigating the CRC microbiome and metabolomic profiles revealed the differential presence of a microbial biofilm layer with a unique metabolomic profile on significantly more right-sided than left-sided cancers. Our group has been at the forefront of the development and application of the metagenomic approaches including the discovery of novel viruses. Combining these techniques with metabolomics profiling can lead to the discovery of novel viral and metabolic triggers of carcinogenesis in the colon.